The present invention is directed to methods and apparatuses for clamping cylindrical workpieces, and more particularly, to methods and apparatuses for clamping and retaining cylindrical workpieces during orbital welding operations.
Orbital arc welding equipment is often utilized to weld tubing and piping used in fluid handling and processing systems. For example, U.S. Pat. No. 5,136,134 to Benway et al. (herein incorporated by reference), and U.S. Pat. No. 4,223,686 to Benway et al. (herein incorporated by reference) both disclose orbital welding apparatuses for welding a pair of tubular workpieces. The apparatuses disclosed therein are primarily directed to systems for welding small diameter tubing in closely confined spaces. The ""134 and ""686 patents disclose a tube clamping assembly for receiving and retaining the tubes to be welded during welding operations. The tube clamping assembly disclosed therein is a generally scissors-type clamp, wherein each tube is held in place between a movable clamp arm and a stationary clamp arm. A tube is mounted in each pair of arms such that they are in end-to-end abutting relation. Once the tubes have been so secured, the orbital weld head is inserted into the tube clamping assembly to carry out the welding operations, and the tubes are welded at their abutting joint. The present invention is directed to improvements in the tube clamping assembly disclosed therein and in other similar tube clamping assemblies.
When welding cylindrical workpieces, the workpieces must be radially and axially aligned such that the end of the first workpiece abuts the end of the second workpiece. However, manufacturing tolerances limit the precision of radial alignment that can be attained in most tube clamping assemblies. Accordingly, there exists a need for a tube clamping assembly capable of ensuring precise radial alignment between the tubular workpieces. An additional problem often arising with existing scissors-type tube clamping assemblies is that the fixed clamp arms, which are typically made integral with the base, are not removable. Accordingly, when the fixed clamp arms are damaged, the entire fixture may have to be replaced. Thus there is a need for a tube clamping device having removable clamp arms, particularly removable stationary clamp arms.
In order to ensure proper alignment of the tubes to be welded, axial movement of the clamp arms should be minimized. It has been found that the clamp arms may flare axially outwardly during clamping of the cylindrical workpieces. The reaction of the radial clamping forces upon the outside diameter of the tube may transfer into an axial force component which causes the clamp arms to flare outwardly. The outward movement may shift the tubes apart so that their butt ends are no longer in contact. Furthermore, it has been found that shrinkage of the weld joint during welding may cause inward movement of the clamp arms. The inward movement may cause the arms to pinch or clamp upon the weld held by the clamping assembly, which can impair the weld head rotor rotation. Accordingly, there is a need for an arrangement for limiting the axial movement of the clamp arms in both the inward and outward axial directions.
Finally, each set of clamp arms should clamp the workpiece with sufficient force such so as to securely grip the workpiece therein to avoid any shifting during welding operations. For example, U.S. Pat. No. 4,868,367 to Benway et al., hereby incorporated by reference, discloses one such apparatus for gripping and retaining a workpiece within a collet. However, existing collets may not provide sufficient contact points between the collet and the tube, thereby allowing the tube to shift with the collet. Accordingly, there is a need for a tube clamping assembly having a collet which ensures adequate points of contact between the collet and the tube.
The present invention is a tube clamping assembly which has an adjustable base to enable radial alignment of the tubes to be welded, has removable/replaceable side plates, provides an arrangement for limiting axial movement of the clamp arms, and has a collet which ensures sufficient points of contact between the collet and the workpieces. More particularly, the present invention provides for a split base having a first portion and a second portion, wherein the first portion is adjustable relative the second portion to ensure proper radial alignment of the tubes to be welded. Using the adjustable features of the present invention, precise radial alignment of the workpieces can be attained. The invention includes a tube clamping assembly comprising a first portion having a base and a clamping device carried on the base, and a second portion having a base and a clamping device carried on the base. The first and second portions are coupled to each other such that the portions may be adjusted relative each other.
The present invention also includes stationary clamp arms that may be removably attached to the base, thereby allowing them to be removed for repair or replacement. In this manner, when the component is damaged it may be repaired instead of having to replace the entire unit. In this embodiment, the invention is a tube clamping assembly comprising a base, and a first movable clamp arm and a first stationary clamp arm coupled to the base for gripping a cylindrical workpiece therebetween. The tube clamping assembly further comprises a second movable clamp arm and a second stationary clamp arm coupled to the base for gripping a cylindrical workpiece therebetween, wherein at least one of the stationary clamp arms is removably coupled to the base.
The present invention also utilizes an arrangement of overlapping and interlocking arc shields to prevent axial movement of the clamp arms in both axial directions. This inventive arrangement minimizes pinching or clamping of the weld head during welding operations, and also ensures that the workpieces remain in abutting relationship to ensure proper welds. In this embodiment, the invention is a tube clamping assembly comprising a base, a first clamping device carried on the base, a second clamping device carried on the base, and locking means for limiting the outward axial movement of the first and second pair of clamping devices.
Finally, the present invention utilizes a collet having a polygonal, preferably hexagonal, shape when in the gripping position. This collet arrangement ensures a minimum of contact points on the tube outer diameter when the tube is in its minimum, nominal, or maximum tolerance condition. These contact points significantly increase the fixture holding rigidity, and thereby minimize the chance for the tube to move after it has been clamped. In this embodiment, the invention comprises a collet for clamping a cylindrical workpiece, the collet comprising a pair of clamp parts each having a clamp surface adapted to engage opposing sides of the workpiece, each clamp surface being generally shaped as half a polygon in side view, the polygon having at least six sides.
Various other embodiments of the invention are described and claimed herein, and other features and advantages of the present device will become apparent from the following detailed description, with reference to the accompanying drawings and claims, which form a part of the specification.